A RAKE receiver is a key technology for implementing W-CDMA systems because of its ability to combat multipath fading. In a wireless medium, the transmitted signal arrives at the receiver via different paths, each having a different (and time-varying) propagation delay and attenuation. The relatively high bandwidth of W-CDMA signal, as compared to the coherence bandwidth of the channel, allows the different multipaths to be resolved. A RAKE receiver combines the signal received from various resolvable paths to provide a diversity gain that results in an improved performance. Thus, to utilize the full diversity, it is important to detect all the resolvable paths with sufficiently high signal-to-interference plus background noise power ratio (SIR).
Path searching is generally defined as the process of determining the position of various multipaths. A path searcher enables the RAKE receiver to coherently combine paths with sufficiently high SIR to achieve diversity gain.
Some additional information regarding CDMA systems in general, and path searchers and RAKE receivers in particular, is provided by the following references, which are all hereby incorporated herein by reference in their entireties, and are referenced throughout the specification using the reference number in brackets:
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